In recent years, due to global warming, in all fields, it has been required to develop eco-friendly products with consideration given to the environment and eco-friendly systems.
In particular, in the field of power supply, since it is directly connected with global warming, power supply that is clean without generation of carbon dioxide is required.
Hence, in recent years, particular attention has been focused on wide use of solar batteries utilizing solar energy which is unlikely to be exhausted and in which there is no worry about generation of carbon dioxide.
Incidentally, there are broadly two types of method of utilizing solar batteries. One method is to provide a power conditioner and utilize generated power in coordination with a so-called alternating-current power supply system.
The other method is to connect generated direct-current power without being processed directly to a direct-current load device and to utilize it.
However, even in either case, it is mandatory to prioritize the generated power from the solar battery and perform maximum power point follow control.
Here, the generated power from the solar battery depends on the amount of solar radiation of sunlight, and it is impossible to stably supply power to a load, using only the solar battery as the power supply. Hence, it is required to use not only a type of solar battery that exceeds an electrical load capacity but also a storage battery.
Moreover, as a method of supplementing the power supply from the unstable solar battery, there is a system that converts general alternating-current commercial power into direct-current power to achieve power coordination and that supplies power to an electrical load from the side of the general commercial power converted into the direct-current power when the amount of solar radiation of sunlight is low or when power generation from the solar battery cannot be expected such as at night (see, for example, patent documents 1, 2 and 3).
However, disadvantageously, the conventional system described above is not designed such that in particular, the power supply from the solar battery is preferentially performed, and that even when the amount of solar radiation is changed, the maximum generated power from the solar battery side can be used.
Conventionally, for example, a maximum generated power point follow control method (generally referred to as a MPPT control method) is performed in which control is performed such that when the solar battery is utilized at the time of charging of a storage battery or for power supply to a power load, the generated power is maximized. As its main control method, there is a known “mountain climbing method” in which the product of an output voltage and an output current from the solar battery is calculated, and an operating point where the resulting value is maximized is gradually searched for and utilized (see, for example, patent document 4).
Furthermore, there is proposed a method of determining the maximum power point with a control method in which in a device for generating hydrogen as the energy source of a fuel battery, a DC chopper is provided between a solar battery and an electrical load with a method where a solar battery voltage is made to follow the optimum operating voltage, attention is focused on the pulsating component of a circuit current and the measurement value of a current sensor is prevented from being saturated (see, for example, patent documents 4 and 5 and non-patent document 1).
Incidentally, in recent years, there has been worry about rapid progress of global warming, and in all fields, it has been required to develop eco-friendly products with consideration given to the environment and eco-friendly systems.
In particular, in the field of power supply, since main power plants and power generation devices are directly connected with global warming, in recent years, a power generation device that is clean without generation of carbon dioxide has been required to be particularly developed.
In recent years, attention has been focused on wide use of solar batteries utilizing solar energy which is unlikely to be exhausted and in which there is no worry about generation of carbon dioxide. In recent years, the development and the wide use of a microgrid network including the solar battery have been required.
Incidentally, the microgrid network refers to an energy system network in which, on a plurality of small dispersed power supplies, power supply storage devices and the like within an energy supply region, effective system operation and control are performed using IT related technologies, and thus efficiency and supply reliability are enhanced. In other words, it can be said to be a small-sized power supply system network.
Its conception has been developed and proposed in the U.S., where there are a large number of small-sized communities separate from normal power systems consisting of large-sized power generation facilities such as nuclear power, thermal power and hydropower and power grids.
Here, as compared with a method of using power from a large-sized power plant, the microgrid network described above is introduced, and thus it is possible to establish an energy supply facility that is a backup at the time of emergency. It is also possible to cut a peak in an existing large-sized power plant. Furthermore, it is possible to reduce the amount of greenhouse gas emitted and energy costs. Effects such as a small amount of energy loss since an energy facility with consideration given to the situation of the region where it is introduced can be established is also expected.
Moreover, in the conventional microgrid, raid variations in load within the network degrade the quality of the power system, such as variations in voltage.